A composite mold can make use of a metal faced mold. The metal can be deposited as a skin such as by metal spraying, sheet forming, casting or machining. Whatever means are used to provide a skin the metal thickness is kept to a minimum and the skin is cradled in a well support composite material including an embedded heater. It is supported as a skin adapted for high temperature operation by way of steel support frames serving to provide for readily matchable mold sets.
As originally conceived solid bonding of the skin to the supporting frame reduced, if it did not actually prevent, allowance for movement between skin and frame to provide. This is desirable in order to allow for a degree of relative movement between skin and frame arising from differential expansion due to different coefficients of thermal expansion between frame and skin.
In our co-pending UK Application No. 9623587.49 (the xe2x80x9cApplicationxe2x80x9d) there is described a process for the manufacture of tooling comprising the use of a thin skin mold supported in a bolster by way of an elastomeric shim over the entire under surface of the skin, the shim being, in turn, supported on an in-fill in the bolster wherein the thin skin is of at least one of the following: vacuum formed thermoplastic sheet; formed metal sheet; cast metal skin; ceramic skin; silicone or similar elastomeric matrix skin; thermoset reinforced or un-reinforced skin.
The application further describes a process for the manufacture of tooling characterized by the steps of: forming on a surface of a master pattern member a skin layer by casting or laminating of plastics material; the skin layer during this stage having an inner face contacting the member and an exposed outer face; depositing on the exposed face of the skin layer a calibration layer of substantially uniform thickness of a material such as wax; the calibration layer during this step having an inner face contacting the sin and an exposed outerface; depositing on the exposed face of the calibration layer a bolster layer of a heat insulating material optionally including means whereby the bolster layer can be heated or cooled or providing for both heating and cooling relative to ambient temperature; shrouding the exposed face of the bolster layer by way of a bolster frame so as to provide between the exposed face of the bolster layer and an inner face of the bolster frame a plenum; filling the plenum with an aggregate material providing for thermal insulation between the bolster layer and the bolster frame; separating the pattern with the skin layer retained thereon from the assembled bolster frame, bolster layer and calibration layer; removing the calibration layer to expose the inner face of the bolster layer; provide a release means on the exposed inner surface of the bolster layer; relocate the pattern with the skin layer retained thereon into the assembled bolster frame and bolster layer; injecting or otherwise locating in the volume left on removal of the calibration layer between the exposed face of the skin layer and the exposed inner surface of the bolster layer a plastics material to provide a locking shim reproducing the exposed face of the skin layer; and operating the pattern from the remainder of the assembly when formation of the locking shim is complete; removing the release means from the bolster layer; locating the skin on the locking shim in the bolster to provide a tool comprising the skin layer releaseably mounted on the bolster layer by way of the locking shim and the bolster layer retained in the bolster frame.
According to a first aspect of the present invention there is provided a method of making tooling comprising the following steps of preparing a master model having a first surface; casting a thin-skinned mold from the first surface of the master model, the thin-skinned mold having an inner surface corresponding to the first surface of the master model and an outer surface spaced from the inner surface thereof; fabricating a bolster in contact with, and releasable from, the outer surface of the thin-skinned mold, which bolster is intended to serve as a support structure for either the thin-skinned mold or a replica thereof; removing the bolster and the thin-skinned mold from the master model and thereafter supporting the thin-skinned mold by means of the bolster, the bolster being in contact with the outer surface of the thin-skinned mold; locating a layer of a thickness calibration material on the inner surface of the thin-skinned mold, the layer corresponding in thickness to an article to be produced by means of the tooling; forming a matching mold set contra half against the layer of calibration material while the calibration material and the thin-skinned mold are supported by the bolster; removing the matching mold set contra half from the combination of the calibration material, the thin-skinned mold and the bolster and thereafter removing the calibration material from the inner surface of the thin-skinned mold; aligning the combination of the bolster and the thin-skinned mold with the matching mold set contra half to define a cavity corresponding to the space previously occupied by the calibration material; coating the surfaces defining the cavity with a release agent and thereafter casting a rigid skin member in the cavity; removing the matching mold set contra half from registration with the combination of the bolster and the thin-skinned mold, and removing the thin-skinned mold from the bolster.
According to a first preferred version of the first aspect of the present invention wherein the provision of a replica of the first female thin skinned mold characterized by the steps of: registering the bolster and rigid skin combination with the mold set contra half to define a cavity defining a mold for a replica of the first female thin skinned mold; and casting a replica in the mold.
According to a second preferred version of the first aspect of the present invention at least one casting process can be selected from a group comprising pouring liquid matrix, injecting a liquid matrix under pressure, injecting a liquid matrix using sub atmospheric pressure; injecting a liquid matrix using both super and sub-atmospheric pressures.
According to a third preferred version of the first aspect of the present invention or any preceding preferred version thereof the bolster and thin skin combination and the mold set contra half provide for heating of a surface to be contracted by material to be cast.
According to a fourth preferred version of the first aspect of the present invention or any preceding preferred version thereof there is provided a step for a surface to be contacted by material for casting of coating with a material selected from a group comprising metal, alloy, ceramic, elastomeric, un-reinforced or reinforced thermoset resin. Typically where a metal coating is to be used the surface is coated by a spraying process. Alternatively the surface is formed by a metal sheet of reduced thickness by comparison with the desired final thin skin and the required thickness is achieved by a layer of a castable matrix attached to the rear side of formed metal sheet.
According to a fifth preferred version of the first aspect of the present invention or any preceding preferred version thereof the step of fabricating the bolster involves a computer numerically controlled machining operation to provide for the subsequent mounting of the item on the bolster.
According to a sixth preferred version of the first aspect of the present invention or any preceding preferred version thereof the item is retained on the bolster by means of a sub-atmospheric pressure.
According to a second aspect of the present invention there is provided a mold tool manufactured according to the method of the first aspect or of any preferred version thereof.
According to a third aspect of the present invention there is provided a product manufactured by means of a mold tool according to the third aspect.
Exemplary embodiments of the new invention will now be broadly described including reference to the accompanying drawings which show steps in a process for manufacturing skins for use in mold sets.